The invention relates to displaying image data on the display of a computer.
As the costs of high-resolution color computer displays and processing power come down, one of the emerging applications for microcomputers is video post production--displaying and editing video images using the display of the computer as the monitor during the editing process. In a computer video editing system, a video source, typically a video tape recorder, is read and stored in digital form on the disk of a computer. The video may be played back, edited, and written back to a video device.
During the tape-to-disk, editing, and disk-to-tape processes, it is desireable to display the video in real time in a display window so that the user can monitor the operation. Keeping the display updated can pose a large computational demand, easily seen in the sheer data volume of a video program--30 frames per second, over 300,000 pixels per frame, and several bits per pixel.
One method for reducing the computation required for monitoring the video data is called subsampling. In subsampled video, each full frame (640.times.480 pixels per frame in the NTSC standard form factor used in U.S., 768.times.576 pixels per frame in the PAL standard used in Europe and Japan) is reduced to a smaller number of pixels, for instance 160.times.120 pixels, which is then displayed in a window on the display screen, permitting other areas of the display to be used for interactive display and control.
In known video editing systems, the CPU of the host computer had responsibility for keeping the video monitor updated at the same time that it kept up with other concurrent tasks, e.g., executing user commands and supervising other system activities